Nobuhide Kasagi

Contribution of Reynolds stress distribution to the skin friction in wall-bounded flows

A simple expression is derived of the componential contributions that different dynamical effects make to the frictional drag in turbulent channel, pipe and plane boundary layer flows. The local skin friction can be decomposed into four parts, i.e., laminar, turbulent, inhomogeneous and transient components, the second of which is a weighted integral of the Reynolds stress distribution. It is reconfirmed that the near-wall Reynolds stress is primarily important for the prediction and control of wall turbulence. As an example, the derived expression is used for an analysis of the drag modification by the opposition control and by the uniform wall blowing/suction.

J081013 Evaluation of exchange current density using three dimensional SOFC anode

Gas diffusion models in the lattice Boltzmann method simulation of SOFC Ni-YSZ anode are evaluated using the reconstructed three-dimensional microstructure by focused ion beam scanning electron microscope. Dusty Gas Model (DGM) and Cylindrical Pore Interpolation Model (CPIM) are applied and evaluated. The predicted overpotentials showed small differences between the models. The exchange current density per unit three phase boundary length is estimated from real electrode microstructure and polarization experiment.

D212 Development of high-performance perfluorinated polymer electret for micro seismic power generation

This paper describes a new high-performance polymer electret with high surface charge density, stability, and high thermal resistibility of electric charge. We found that MEMS-friendly perfluorinated polymer CYTOP shows excellent electret properties and the thermal stability by doping silane coupling reagent into the polymer. The charge density of 1.5 mC/cm, which is 1.6 times larger than that of the undoped CYTOP, has been obtained on 16 μm-thick film. The power generation of 0.7 mW at a low seismic frequency of 20Hz was also accomplished, which is about two and a half times higher than the reported data.

D208 Basic Study of Selective Emitter Using Surface Micro Cavities

Si microcavity coated with Ti film have been developed as a selective emitter for high-efficiency micro thermophotovoltaic (TPV) power generation system. Emittance of two cavities with the similarity shape but with different dimensions is compared. We demonstrate that an emittance peak appears near the wavelength of 3 μm, which is close to the designed value, and the peak is much higher than the emittance of large cavity. Therefore, not only for the effect of surface area increase, but also the resonance of electromagnetic modes plays an important role in the modification of emittance.